The present invention relates to an elastic bushing, particularly for use in the goods transport vehicle sector.
More specifically, the invention relates to elastic bushings that are used to connect an axle or a pin, which is subject to rotations and/or vibrations, to a frame or support. A typical example is represented by the anchoring of the eye of a leaf spring used in shock absorbers to the chassis of commercial vehicles, vans, trucks, etc.
Bushings are known, for example, that essentially comprise an inner cylindrical tubular element made of metal, onto which a rubber elastic ring is vulcanized, which in turn is fixed by means of vulcanization or by interference to an outer cylindrical tubular element, made of metal and coaxial to the first one.
In this case, assembly of the bushings is achieved by coupling by interference the outer metallic cylindrical tubular element to the assembly seat, after boring the latter.
This construction solution has a high risk of torsional fatigue failure of the rubber ring with a consequent reduction in the lifetime of the bushing.
Furthermore, bushings constructed in this manner do not eliminate the inconveniences linked to the need to prepare seats suitable for the assembly by interference of the outer metal tubular element, with consequent high costs due to the mechanical working, to the difficulty of said assembly, and to the high weight and cost of said bushings.
From utility model application no. CR97U000005 by the same applicant, a particular type of bushing is known, essentially comprising an inner cylindrical tubular element made of self-lubricating material, onto which a ring made of rubber or another elastically deformable material is fitted; the outer cylindrical surface of said ring is provided with ribs arranged longitudinally, substantially parallel to the axis of the bushing.
These ribs enable connection by friction by means of the forced fitting of the bushing into the circular seat provided on the element to be connected, without the need for overly precise working of the seat and without having to apply excessive force for assembly.
The pin is free to rotate on the inner surface of the element made of self-lubricating material, and consequently does not transmit any torsional stress to the rubber ring, whose job is therefore only to absorb thrusts and stresses in a radial direction.
However, this type of bushing, although not requiring precise mechanical working and restrictive dimensional tolerances, does have certain limits that are manifested during assembly of the bushings into their respective seats.
These ribs project considerably from the side surface of the rubber ring, constituting a notable radial size and, moreover, extending constantly beyond the dimension of the seat into which the bushing has to be inserted: the operation to insert the bushing into the assembly seat is therefore difficult and requires the use of lubricants to facilitate sliding of the parts, thereby slowing down the assembly operations.
Since these ribs are of the discrete type, they result in discontinuous adherence between the side surface of the rubber ring and the inner wall of the assembly seat.
A further inconvenience consists in the fact that, due to the high assembly force required, the rubber ring is subject to considerable deformations, which may result in expansion and stretching of the rubber, and which could even break the collar of the cylindrical tubular element made of self-lubricating material, thereby requiring the replacement of the bushing.
Furthermore, if the elastic ring in deformable material were freely fitted onto the self-lubricating element and high radial loads were reached during bushing operation, the cylindrical tubular element could rotate with respect to the ring made of deformable material, causing noise and no longer correctly absorbing the thrusts and radial stresses.